This invention relates to a clinometer provided with a level vial filled with transparent liquids and a bubble, and a projector for irradiating the level vial.
Heretofore, there has been known a clinometer as shown in FIG. 16 and described in Japanese Patent Application Early Laid-open Publication H2-42310.
Referring to FIG. 16, a level vial 1 includes a transparent vessel 3 of which an upper inside wall is formed spherically hollow, and a transparent liquid 4 and a bubble 5 inside the vessel 3. Under the level vial 1 are disposed a light source 6 such as a light emitting diode, and a lens 7 for converting the light emitted from the source 6 into parallel rays of light. Over the level vial 1 is disposed a light receiving element 8 for receiving a bubble shadow 5a (see FIG. 17). Numeral 9 designates an arithmetic unit for calculating an inclination of the vessel 3 from an amount of light received by the element 8.
The element 8 consists of light receiving portions 8a to 8d, each area of which is equalized, each of which extends along the X-axis or Y-axis as shown in FIG. 17. When the vessel 3 has no inclination, the bubble 5 is located at the center of the vessel 3 and hence the center of the bubble shadow 5a as drawn by a stitch line coincides with the origin of the axes. Each amount of light of the portions 8a to 8d is equal to each other at that time.
When the bubble shadow 5a moves from the center to a position as a solid line in proportion to an inclination of the vessel 3, its movement varies each area of the potions 8a to 8d shaded by the bubble shadow 5a. The variation of the area signifies that of an amount of light received by each light receiving portion 8a to 8d. Therefore, an inclination of the vessel 3 can be calculated from each amount of light of the portions 8a to 8d. In other words, the angle of an inclination corresponds to the variation or rate of change of an amount of the received light. The arithmetic unit 9 can calculate the angle of an inclination of the vessel 3 on the basis of the variation.
Conventional clinometers calculate an inclination in terms of an amount of light received by the light receiving element as mentioned above. However, a diameter of the bubble 5 in the vessel 3 fluctuates according to air temperature, so that an amount of light received by the portions 8a to 8d varies. Accordingly, they had to compensate according to air temperature in order to gain the accurate angle of an inclination of the vessel 3. Further, they have several problems such as nonuniformity of light emitted from the source 6 or irregular sensitivity of the light receiving element 8.